Prior art UV curable paints are less adherent to ionomer resins and urethane resins commonly used as the cover of golf balls. The cured coatings of such UV curable paints suffer from the problem of poor bond strength to ionomer resins and urethane resins.
Crast et al., U.S. Pat. No. 6,165,564 discloses to add a carbodiimide resin to a UV curable coating as an adhesion improver. There is still left a room for improvement in the adhesion between the coating and the golf ball surface.
With the desire to improve the adhesion of UV curable paint to golf balls, attempts were made to blend in the UV curable paint a component which is expected to achieve an improvement in adhesion, typically an isocyanate compound, but failed to achieve a practically acceptable level of adhesion.
Since these approaches originate from the technique of improving the adhesion of two-part cure type urethane coating compositions commonly used in golf balls, they are not effective for improving the adhesion of UV-curable paints which rely on a different reaction scheme from the urethane.